1. Field of the Invention
The present invention relates generally to methods and apparatus for removing contaminants from a moving workpiece and, more particularly, to methods and apparatus for wiping contaminants from a rolled metal strip while the strip is being cold rolled.
2. Description of the Prior Art
In cold rolling of metal strip, lubricant-coated strip passes through one or more mill stands in order to temper or reduce the strip to a desired thickness. When rolling, however, there normally occurs a "plate-out" effect, i.e., in the roll bite, water is squeezed out of the oil emulsion, whereby contaminants such as minute dirt particles tend to adhere to the residual oil and accumulate on the strip. Consequently, passage of the accumulated contaminants through the roll bite frequently cause "rolled-in" defects to be formed on the strip surface. The lubricant can also become polymerized when subjected to the elevated temperatures and high pressures of rolling the strip to finished gauge.
A number of ways and means have been introduced for lubricating while minimizing excess lubricant that is carried by a strip during cold rolling and/or final coiling thereof.
The earliest attempts at reducing the quantity of lubricant carried by the strip involved using bar wipers. For example, simply placing a rubber hose wiper across the width of the strip acts as a squeegee or striking the excess lubricant material from the moving strip. Along with failing to completely remove the lubricant carried by the strip, rubber hoses and other bar wipers required frequent changing because of their inherent low durability, and the strip commonly became etched or marked by stray waste chips of metal or other particles which may become embedded in the hose.
To overcome many of the problems related to bar or rubber hose wipers, metallic roller wiping systems have been developed which generally include three metallic wiper rollers (one positioned above the strip and two below, or vice versa) extending transversely to the moving strip.
Three-roll wipers embodying metallic wiper rollers have been used for over 10 years on some United States and many European Sendzimir mills (Z-mills) for rolling stainless steels. Their advantages relative to bar wipers (i.e., rubber hose type) are that both lost time due to frequent changing of wiper hoses and strip marking caused by chips which become embedded in the hoses are eliminated.
Improved three-roll metallic wiper assemblies including wiper rollers that are backed-up, including smaller diameter wiper rolls than those of conventional three-roll design are commercially available under the tradename, Pollastrelli. The smaller diameter rollers wipe more effectively and can be changed very quickly by hand. Also a spring-loaded support roller arrangement present in advanced three-roller wiper designs, in conjunction with the more flexible smaller diameter wiper rollers, ensures much more uniform wiping pressure, even if the strip profile is not uniform (as occurs frequently), thereby ensuring uniform wiping at all points across the strip width. In addition, because the wiper assemblies are lighter, it is usually possible to provide a floating arrangement whereby the wipers will float up and down to follow the strip pass line.
Non-metallic roller wiper systems and lubricant vacuum systems are also known, each of which possess particular advantages and disadvantages.
Notwithstanding their individual and collective advantages, however, the known systems for wiping lubricant carried by a moving metal strip during cold rolling thereof fail to completely remove all oil lubricant from the strip. Therefore, they likewise fail to remove and prevent accumulation of lubricant contaminate matter which could become rolled into the strip.
It is therefore an object of the present invention to provide a rolling mill strip wiper assembly for effectively removing and preventing virtually all lubricant deposits and accumulations of contaminate matter borne by the strip.
Another object is to provide an uncomplicated wiper assembly for applying a liquid to a moving metal strip which assembly can be easily changed.
Still other objects and advantages of the present invention will become apparent in light of the attached drawings and written description of the invention presented hereinbelow.